Dr. Horrible's Sing-Along Blog: Who's Who?

Neil Patrick Harris

HERE HE PLAYS: Dr. Horrible — a wannabe evil mastermind with “a Ph.D. in horribleness,” a desire to destroy Captain Hammer and a debilitating crush on do-gooder Penny; those not attuned to the evil underground know him as Billy

EXTRA HORRIBLE TIDBIT: Horrible’s Death Ray is actually a repurposed prop from Firefly, turned upside down and embellished a little.

Nathan Fillion

YOU KNOW HIM AS: Rick Castle — Castle‘s author of mysteries, consultant on police cases, poker player and new love interest of a certain lovely lady cop

Felicia Day

YOU KNOW HER AS: Holly Marten — Eureka‘s rocket scientist, who showed up in several iterations throughout the sci-fi series; she’s also Codex in The Guild, the Web series she created, and she’s appeared in other Joss Whedon projects like Buffy the Vampire Slayer and Dollhouse

HERE SHE PLAYS: Penny, a quiet woman looking to make her city a better place, particularly through her volunteer work at a local soup kitchen/homeless shelter

EXTRA HORRIBLE TIDBIT: On her Web site, Day notes that the soundtrack’s success “made me a Billboard Top 40 artist, which makes me giggle with the absurdity of it.”

Simon Helberg

YOU KNOW HIM AS: Howard Wolowitz — The Big Bang Theory‘s bowl cut-sporting aerospace engineer who recently became both a husband and an astronaut

HERE HE PLAYS: Moist, Dr. Horrible’s perpetually sweaty henchman

EXTRA HORRIBLE TIDBIT: Though unfamiliar with Joss Whedon’s work, Helberg told the Huffington Post he took the gig because he knew Zack and Jed Whedon (Joss’ bros, who co-wrote the project with him and Jed’s wife Maurissa Tancharoen) from high school.

Now that you’ve got the basics, hit the comments with all of your horrible thoughts!